Image synthesis, which may be used, for example, when creating computer graphics for video games, web pages and the like, is typically carried out using techniques based either on analytical models or on acquired images of a physical object. Not only must the synthesized images accurately represent the shape and color of the physical object, the synthesized images must accurately represent the ways in which the physical object reflects light (e.g., the radiance of the object). As described below, techniques based on analytical models, as well as those based on acquired images, have shortcomings.
One technique that is based on analytical models is performed using global illumination techniques, which combine light transport simulation with analytic material reflectance models to achieve simple, compact and flexible representation of three-dimensional (3D) scenes or objects. Global illumination techniques are computationally efficient once the analytical models have been developed, and, therefore, are easily rendered to create real-time graphics. However, analytical material reflectance models and, therefore, global illumination imaging based on such reflectance models are costly to compute and difficult to develop.
Image-based techniques have recently emerged as an alternative approach to creating costly analytical models for realistic image synthesis. Image-based techniques synthesize images based on graphical information of an object. Such graphical information may include pixel information of the object from a digital camera or from a scanner. Image-based techniques represent radiance data directly in a sample-based format without using any analytical models and, therefore, have gained popularity because they promise simple acquisition of 3D models and an accurate portrayal of physical objects and the physical world.
Presently, image-based techniques process data from, for example, a number of digital camera acquisitions taken from different angles while a lighting source is located in a fixed position. For example, an object may be digitally photographed from thirty or more different angles or positions, while a light source illuminating the object is held in a fixed position. As will be appreciated, the information of an object developed by the digital camera may occupy several megabytes (MB) of storage space, making it difficult or impractical for a website or a computer graphics intensive game to render the object in real time. Additionally, the fixed lighting position leads to acquired images having fixed illumination thereon. Such images do not always realistically reproduce how the object would appear under diverse lighting conditions.